1. FIELD OF THE INVENTION
This invention relates generally to the fields of biochemistry and molecular biology and more specifically to cell adhesion molecules.
2. BACKGROUND INFORMATION
The early stages of pregnancy involve fertilization of an egg by a sperm, followed by cell division and implantation of the embryo into the uterine cell wall. The inability of the embryo to properly implant in the uterus is a significant cause of pregnancy failure following in vivo or in vitro fertilization. The early events of implantation are characterized by an initial attachment of the embryo's external cell lining (trophoblast layer) to the cells lining the uterus (endometrial epithelium) followed by or in parallel with adhesion of these two cell types. The molecular events involved in the early steps in implantation are not well understood.
Embryo attachment and adhesion to the uterine endometrium is unusual in that cells from these two sources adhere at their apical surfaces. In contrast, most other epithelial cell interactions adhere at their basal and lateral cell surfaces. The unique ability of trophoblast and endometrial cells to adhere may result from apical display of adhesion molecules normally located at basal and lateral surfaces. Alternatively, adhesion of these cell types in implantation may be mediated by unique cell surface molecules.
Recent experiments suggest that certain endometrial tumor cell lines express characteristics associated with implantation-receptive endometrial tissue. In these experiments, trophoblast cells derived from germ cell tumors adhered to monolayers of endometrial adenocarcinoma cells via their apical cell surfaces. Morphological analysis of the adhering cell surfaces showed characteristics in common with early stage implantation. However, the molecules involved in the critical early adhesion step of embryo implantation were not identified. Thus, a need exists to identify the molecules responsible for adhesion of the embryo to the uterine lining. The present invention satisfies this need and provides related advantages as well.